Schuster and colleagues are now analyzing the woolly mammoth genomes to help figure out exactly what caused the mammoths' extinction at the end of the last ice age about 10,000 years ago.

The comparisons will show when genetic diversity declined—a sign of population weakness.

This date can then be correlated with other events that might have led to the mammoths' downfall, such as climate warming, the arrival of humans, or outbreaks of disease.

What's more, Schuster noted, his team found that the same technique of retrieving ancient DNA from hair works well with hair samples from other animals that coexisted with mammoths.

"If you would find that the genetic diversity collapsed not only for one species [the mammoth] but also for several species, then this will help you to understand what the entire ecosystem looks like," he said.

In addition, the technique could be used to retrieve a complete nuclear genome of an extinct animal, Schuster said.

Michael Hofreiter is an evolutionary geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who led the team that retrieved the first woolly mammoth genome from bone.

He said the new technique reported in Science is an excellent advance, particularly for robust population genetic analyses—as long as hair is available.

"For mammoths it's great, but for most extinct animals we don't have hair samples," he said.

For example, his group is now working on ancient DNA from cave bears, which lived in Europe and also went extinct about 10,000 years ago.

Hundreds of thousands of cave bear bones are available for study, he said, "but there's not a single hair preserved."

Schuster and colleagues, however, are undeterred.

They note that one of the mammoth genomes they sequenced is from the famous Adams mammoth, which was pulled from the permafrost in 1806 and has been kept in a museum at room temperature ever since.

"[This] puts a large number of collections stored in natural history museums within reach of molecular genomic analysis," the team writes in the paper, "and may also allow us to add molecular-genetic data to the collections of Charles Darwin, Alexander von Humboldt, and Carl von Linné [also called Linnaeus]."